Guidelines for Tree Risk Assessment and Management Arrangement
On an Area Basis and on a Tree Basis
GREENING, LANDSCAPE AND TREE MANAGEMENT SECTION
DEVELOPMENT BUREAU
December 2012
GUIDELINES FOR TREE RISK ASSESSMENT AND MANAGEMENT
ARRANGEMENT ON AN AREA BASIS AND ON A TREE BASIS
CONTENTS
1.
2
3.
4.
5.
6.
7.
Background ……………………………………………………………..
Purpose of the Guidelines ………………………………………………
Tree Risk Assessment on an “Area Basis”……………………………...
Tree Risk Assessment on a “Tree Basis”………………………………..
Audit Inspection .………………………………………………………..
Development Bureau’s Tree Register ………………………………......
Points to Notes – Remedial/Risk Mitigation Measures and
Compensatory Planting ……………………………………………….…
Page
1
2
2
14
30
30
31
Annexes
A. Form 1: Tree Group Inspection Form
B. Form 2: Tree Risk Assessment Form
C. Pictorial Guide For Tree Maintenance To Reduce Tree Risks & Supplementary Photos
D. Guidelines on Photo-Taking of Tree Conditions in the Process of Tree Risk Assessment
Tree Management Office
Greening, Landscape and Tree Management Section
Development Bureau
www.trees.gov.hk
Greening, Landscape and Tree Management Section
Arrangement
Development Bureau
Guidelines for Tree Risk Management and Assessment
Guidelines for Tree Risk Assessment and Management Arrangement
on an “Area Basis” and a “Tree Basis”
1.
Background
1.1
Pursuant to the recommendation in the Report of the Task Force on Tree Management –
People, Trees, Harmony published on 29 June 2009 and Coroner’s Court recommendation on fatal
tree incident at Yuen Chau Kok dated 12 July 2011, the Development Bureau (DEVB) has
introduced and updated a set of new tree risk assessment arrangements since January 2010 for
implementation by the tree management departments in order to better protect public safety. These
arrangements, which were formulated with reference to the international best practices with due
consideration to the circumstances in Hong Kong, are based on a dual approach –
(a)
“Area Basis” assessment – departments concerned will first identify those areas
where members of public will be affected if a tree fails; and
(b)
“Tree Basis” assessment – once an area is identified, staff in the department
concerned will identify those trees which may be problematic/important, and assess
their conditions in accordance with a standardised format with particular emphasis on
the risk angle. Old and Valuable Trees (OVTs) will as a rule be included for close
monitoring.
1.2
Appropriate risk mitigation measures will then be identified having regard to the specific
conditions of individual trees that pose a risk to public safety. As recommended by the Task Force,
in case of conflicts between tree preservation and public safety, the latter should be given a higher
priority.
1.3
In view of the varying circumstances of the tree management departments and resource
limitations, the Task Force considered it necessary to allow suitable flexibility in the implementation
of the tree risk assessment arrangements across departments. It is envisaged that over time,
Government will be able to systematically build up a comprehensive database of the conditions of
trees located on government lands for guiding the formulation of necessary remedial actions and risk
mitigation measures as well as facilitating future monitoring of the conditions of these trees.
1.4
In the light of the previous practical experience gained from the tree risk assessment
exercise, the Tree Management Office (TMO) of DEVB has updated the Guidelines for Tree Risk
Assessment and Management Arrangement for implementation.
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2.
Guidelines for Tree Risk Management and Assessment
Purpose of the Guidelines
2.1
Risk is the combination of the likelihood of an event and severity of the potential
consequence. A systematic process for tree risk assessment is essential to identify, analyze and
evaluate tree risk. The Guidelines elaborate on the methodology for demarcating tree risk
management zones on an “Area Basis” and for carrying out tree risk assessment on a “Tree Basis”,
including the application of the tree assessment forms Form 1 – Tree Group Inspection Form (in
Annex A) and Form 2 – Tree Risk Assessment Form (in Annex B).
2.2
Tree risk management is not a one-off exercise. It constitutes a professional approach to
tree management and helps ensure the long-term sustainability of our trees. The methodology set out
in the Guidelines assist departments in identifying trees with health and/or structural problem in a
systematic manner so that remedial actions can be taken in a timely manner to alleviate the potential
risks.
3.
Tree Risk Assessment on an “Area Basis”
3.1
Government is striving to uplift the quality of our living environment through active
planting, proper maintenance and preservation of trees together with other vegetation. As trees are
living organisms, their health and structural conditions will change with their life cycle and their
surroundings, especially in inclement weather. Government has a duty of care on the proper
maintenance of trees for the protection of public safety, through implementing the tree risk
assessment and management.
3.2
With over millions of trees in urbanized areas of Hong Kong, it is not practical, if not
impossible, to cover every tree with an individual tree assessment. Therefore, the objective of the
“Area Basis” assessment is to focus on areas where targets will be subject to risk of
significant/unacceptable harm in the event of a tree failure so that the tree management departments
will allocate their resources to these areas with higher priority for more effective tree risk
management.
3.3
3.3.1
The process of “Area Basis” tree risk assessment
The “Area Basis” tree risk assessment aims to:
(1)
Identify areas where failure of tree will pose a hazard to public safety or cause
disruption to human activity; and
(2)
Prioritise effort of tree risk management according to the frequency of use of the
area.
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3.3.2
Guidelines for Tree Risk Management and Assessment
Targets are people, property, or human activities that could be injured, damaged, or
disrupted by a tree failure e.g. partial or complete closure of road traffic. A tree cannot be a
hazard without the presence of a target. For sites managed by departments, tree risk
management zones can be determined based on the intensity of use in target areas which
can be affected by tree failure.
Intensity of Use in Target Area
Tree Risk
Management Zone
Intensive Use
Areas of high traffic flow and high pedestrian flow such as public
Category I
parks, playgrounds, crowded streets, busy carriageways, schools,
etc.
Infrequent Use
Areas of low traffic flow and low pedestrian flow such as road verges
Category II
of limited access, countryside roads, village footpaths, etc.
Rare Use
Areas with very rare public access such as inaccessible areas,
Category III
remote countryside slopes, dense woodlands, maintenance access
not open for public, etc.
Determination of tree risk management priority areas
Identify target areas
& intensity of use in
target areas
Sites under
management
Category I Zone
Tree Risk
Management Priority
Area
Category II Zone
Tree Group
Inspection
Category III Zone
Selection of trees for
detailed risk
assessment
Tree Risk
Management
Secondary Priority
Area
Assessment on an “Area Basis”
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3.3.3
Tree management departments are required to categorise sites under their management into
tree risk management zones, such as Category I Zone, Category II Zone and Category III
Zone being an “area basis” approach having regard to the intensity of use in the target
areas. Category I Zone is designated as tree risk management priority area, whereas
Category II Zone and Category III Zone are designated as tree risk management secondary
priority areas. Such site categorization covers sites temporarily under the management of
works departments during the course of public works projects. Works departments
should approach the departments that previously managed the site for records of previous
tree inspections to familiarize themselves with pre-existing tree conditions.
3.3.4
Tree risk assessment should be carried out regularly (at least annually) for Category I Zone
and when necessary to cope with the changing conditions of the trees. We recommend tree
management departments to carry out tree risk assessment for Category II Zone and
Category III Zone when they have already completed tree risk assessment for all trees in
Category I Zone and if resources permit. For Category II Zone, tree risk assessment to be
programmed for at least every 3-5 years per cycle is recommended.
3.4
Working examples of demarcation of tree risk management zone on an “Area
Basis”
3.4.1
An example in a country park
Example – AFCD case Shing Mun Country Park
Step 1: Desktop Demarcation
Step 2
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Step 2
Step 3
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Guidelines for Tree Risk Management and Assessment
Step 4
Step 5
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3.4.2
Guidelines for Tree Risk Management and Assessment
An example in a public park
Example – LCSD case Kowloon Park and along Nathan Road, Tsim Sha Tsui
Step 1: Desktop Demarcation
Step 2
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3.4.3
Guidelines for Tree Risk Management and Assessment
An example in a public housing estate
Example – HD case Lei Muk Shu Estate, Kwai Chung
Step 1: Desktop Demarcation
Step 2
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Step 3
Step 4
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3.4.4
Guidelines for Tree Risk Management and Assessment
An example in a water service reservoir
Example – WSD case – Tsuen Wan No. 2 Fresh Water Service Reservoir, Kwai Chung
Step 1: Desktop Demarcation
Step 2
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3.4.5
Guidelines for Tree Risk Management and Assessment
An example along a highway
Example – HyD case – a site along Tuen Mun Road
Step 1: Desktop Demarcation
Boundary of Tuen Mun Road Step 2
HyD tree maintenance boundary ‐ expressway boundary and SIMAR slopes Unallocated government land under LandsD’s jurisdiction 11
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Step 3
Delineated Cat. I Zone
z
z
trees next to busy expressway prominent target due to busy traffic Step 4
Expressway boundary and SIMAR slope under HyD’s jurisdiction
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A SIMAR slope maintained by HyD
3.4.6
An example of a construction site
Example – CEDD case – construction site in Central
3.4.6.1
As a general principle, the party that is maintaining the tree when risk assessment is
required should be responsible for undertaking the tree risk assessment. After construction,
if a works department is still maintaining a tree during the establishment period or the
aftercare period for Old and Valuable Trees, the works department concerned should be
responsible for the tree risk assessment. If a tree has been handed over to the maintenance
department for long-term maintenance after construction, the maintenance department
concerned should be responsible for the tree risk assessment.
3.4.6.2
When carrying out tree risk assessment, if the site (or part of the site) falls in a Category I
Zone, the department should proceed with a tree group inspection (Form 1) and, where
appropriate, a detailed assessment using Form 2 for individual trees as necessary.
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3.4.6.3
Guidelines for Tree Risk Management and Assessment
Construction sites are spaces that are in transition from an original use to a new use. In
many cases a full tree survey may exist for the project that is under construction and this
may be used to understand the baseline condition of the trees on the construction site.
3.4.6.4 In undertaking tree risk assessment the following considerations should be taken into
account:
3.4.6.5
4.
♦
Trees on site are normally hoarded off to protect them and this reduces the risk if areas
within the hoarding area are not accessible, i.e. no target.
♦
The location of the trees on the site influences the risk. Trees located fully within the
site and potentially affecting only the site area may be classed as Category II Zone.
Trees located on site but potentially affecting a public area off site (e.g. adjacent to a
public roadside) should be classed as Category I Zone.
Trees in construction sites may be subject to higher stress than normal due to changes in
their original environmental conditions (e.g. changes in water table levels, dust, vibration,
soil compaction, etc.) therefore more frequent (e.g. monthly) risk assessment should be
conducted in the initial stage of the operation phase of the new development.
Tree Risk Assessment on a “Tree Basis”
4.1
Once a tree risk management priority area is identified, staff in the department concerned
should identify those trees which may be problematic/important, assess their health and structural
conditions systematically and professionally with particular emphasis on the risk perspective, and
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record the inspection findings using standardized forms promulgated by the TMO (i.e. Form 1 and
Form 2)
4.2
Procedure of tree risk assessment on an “Area Basis” and a “Tree Basis”
4.3
Use of Form 1 – Tree Group Inspection Form
4.3.1
For trees in the tree risk management priority area, they will first be screened by way of a
tree group inspection using Form 1 - Tree Group Inspection Form. For users with Tree
Management Information System (TMIS) accounts, the use of Form 1 under the TMIS
format is recommended. Tree group inspection is an important step to screen out
problematic trees and those require special care. The use of binoculars in tree group
inspection by obtaining a closer view of conditions of the canopy at higher level, when
required, is desirable. To safeguard the quality of the tree group inspection, the size and
coverage of each tree group should not be excessively large. Depending on the
departmental needs and on-site situations, Inspection Officer should duly consider the
limitations of visual tree assessment when devising the size and coverage of each tree
group. The Inspection Officer can delineate the boundary of tree groups by location
types, such as public park, SIMAR slopes, tree pits, etc.
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4.3.2
Guidelines for Tree Risk Management and Assessment
Although Form 1 does not require details of individual trees in a tree group to be recorded,
the Inspection Officer should inspect each tree in the tree group systematically, paying
particular attention to potential tree hazards due to the health conditions or structural
conditions of each individual tree. While not all trees falling into the tree risk
management priority area need to be covered by detailed tree risk assessments using Form
2, for the purpose of identifying potential tree hazards for mitigation action, we encourage
tree management departments to build up an inventory of these trees over time to facilitate
future tree management.
For tree risk
management purpose in the present exercise, all
trees meeting the following criteria and located
on government land are required to be assessed
with a Form 2 – Tree Risk Assessment Form –
(i)
Old and Valuable Trees (OVT),
(ii) Stonewall trees, and
(iii) Tree with mitigation measures outstanding
/ require continuous monitoring. Please
refer to Annex C for an illustrated guide on
identification of tree hazards.
Stonewall trees on Forbes Street
4.3.3
Trees meeting the criteria of “Trees on complaint list with structural or health
problems”, “Mature Trees belonging to species with brittle wood structure and
having unsatisfactory health or structural conditions with failure potential” “Tree
with major defects or health problems” and “Tree growing in very stressful site
conditions with failure potential” should be identified for implementing proper
mitigation measures and/or monitoring. Where necessary, detailed tree risk assessment
should be carried out to identify the tree hazard and appropriate mitigation measures,
Form 2 or other similar report formats can be used for this purpose.
4.3.4
Explanatory notes for Form 1
4.3.4.1
General Information
♦
The main objective is to initially screen trees, keep records for further monitoring, and
identify tree hazards for appropriate remedial measures or more detailed individual tree
risk assessment using Form 2.
♦
Recent tree survey details, if available (i.e. details of surveys conducted within 2 years
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before the date of the Form 1 inspections), of the site concerned could be consulted for the
required information in “General Tree Information” upon verification or updating. The
relevant tree survey report should be attached to Form 1 for reference. The Inspection
Officer should refer to the records of previous inspections conducted for the same site
and/or trees in the same site, as applicable, to help identify changes in the site conditions
or tree conditions that warrant special attention.
Training / Qualification
The “Inspection Officer” usually is the frontline staff member who conducts the tree risk
assessment. To be qualified as “Inspection Officers” for Form 1, they are required to
meet both requirements on training / qualification AND work experience:(a) have attended and completed the following training courses organised by the TMO:1. Comprehensive Tree Risk Assessment and Management Training Course with
assessment organised; OR
2. Refresher Course with assessment; OR
(b) have undertaken equivalent departmental training recognised by the TMO; OR
(c) have successfully undertaken training programmes recognised by the TMO, such as
Tree Risk Assessment Course and Examination (TRACE) organised by the Pacific
Northwest Chapter of the International Society of Arboriculture (ISA) or Professional
Tree Inspection by LANTRA Awards; OR
(d) have valid qualifications or certifications awarded by recognised institution or
industry organisation on arboriculture, such as Certified Arborist of ISA, Registered
Arborist (Level 3 or above) of Arboriculture Australia, Technician Member or above
of the Arboriculture Association of the United Kingdom, Accredited Arboricultural
Practitioner of the Hong Kong Institute of Landscape Architects, Professional
Diploma Programme in Arboriculture of the Chinese University of Hong Kong, etc.
Work
Experience
♦
Have at least 2 years of work experience in tree care and are familiar with tree risk
assessment/management.
♦
For outsourced tree inspection works, the consultant/contractor staff can serve as the
“Inspection Officer” to conduct the tree risk assessment, whereas the same requirements
on training / qualification AND work experience apply.
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♦
Guidelines for Tree Risk Management and Assessment
The “Endorsement Officer” is the supervisory/managerial staff at a rank higher than
Inspection Officer who oversees the tree risk assessment process. To be qualified as
“Endorsement Officers” for Form 1, they are required to meet the requirements on training
/ qualification:-
Training / Qualification
(a) have attended and completed the following training courses organised by the TMO:1. Comprehensive Tree Risk Assessment and Management Training Course with
assessment organised; OR
2. Refresher Course with assessment; OR
3. Tree Risk Management Training Course with assessment; OR
(b) have undertaken equivalent departmental training recognised by the TMO; OR
(c) have successfully undertaken training programmes recognised by the TMO, such as
Tree Risk Assessment Course and Examination (TRACE) organised by the Pacific
Northwest Chapter of the International Society of Arboriculture (ISA) or Professional
Tree Inspection by LANTRA Awards; OR
(d) have valid qualifications or certifications awarded by recognised institution or
industry organisation on arboriculture, such as Certified Arborist of ISA, Registered
Arborist (Level 3 or above) of Arboriculture Australia, Technician Member or above
of the Arboriculture Association of the United Kingdom, Accredited Arboricultural
Practitioner of the Hong Kong Institute of Landscape Architects, Professional
Diploma Programme in Arboriculture of the Chinese University of Hong Kong, etc.
♦
4.3.4.2
♦
4.3.4.3
♦
For outsourced tree inspection works, the supervisory/managerial staff of the
consultant/contractor firm can serve as “Endorsement Officers”, whereas the same
requirements on training / qualification apply.
Location Information
This information is self-explanatory. Additional information that may help identify the
location of the tree group (e.g. lamp post no., SIMAR slope no., other prominent
landmarks nearby, etc.) should be recorded in the “Others” field.
General Tree Information
Main tree species in the group (DBH ≧ 95mm) and minority tree species of
significant size (i.e. approximately DBH ≧ 300mm) – an indicative description of the
diversity and distribution of tree species in the tree group. The approximate quantity (in
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number) of each tree species in the tree group should be recorded under “Approximate
number of trees”.
♦
Range of tree height - an indicative description of the tree height of each specified tree
species.
♦
Overall health condition and overall structural condition - (Refer to Annex C –
‘Pictorial Guide for Tree Maintenance to Reduce Tree Risk’). These two sections
record the overall health and structural conditions of each specified tree species.
♦
Other remarks - Additional information on trees which require further attention should
be recorded in this column to facilitate identification of appropriate follow-up action and
future monitoring of tree conditions.
4.3.4.4
Target
♦
Target - Targets are people, property, or human activities that could be injured, damaged,
or disrupted by a tree failure. For the roadside case, with reference to the prevailing
international practices, the possible Tree Fall Zone (TFZ) is defined as 1.5 times of the
height of a tree planted along the roadside kerb or slope. The TFZ should be adjusted
according to the angle of the lean of a tree and site condition (e.g. the gradient of the slope
where the tree is located.)
♦
Does target exist? - The Inspection Officer should consider if any target exists within the
target area of the tree group.
♦
Can target be moved? - For example, a picnic table beneath a defective tree inside a
country park can be moved to other areas to minimize the presence of the target near the
tree.
♦
Can use of the site be restricted? - For example, fencing off the site to avoid presence of
target beneath the tree.
♦
Frequency of use of location
— Constant use - For example, presence of a house next to a tree is “constant use” as
the house is static and a pavement along Nathan Road with very busy pedestrian and
vehicular flow is under “constant use”.
—
Frequent use - For example, a park with regular visitors is “frequent use”.
—
—
Intermittent use - A recreational cycling path used intermittently is an example.
Occasional use - For example, a maintenance path with restricted access and limited
to use by the maintenance party is “occasional use”.
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4.3.4.5
Identification of Trees for Remedial Action or Detailed Tree Risk Assessment
(Form 2)
During the tree group inspection (Form 1), it is essential to identify potential tree hazards
so that remedial action or detailed tree risk assessment (Form 2) for the trees concerned
can be carried out in a timely manner. The identification process should cover the
following types of trees:
♦
Old and Valuable Trees (OVTs) and Stonewall Trees - OVTs and stonewall trees are
generally regarded as important features of high conservation, heritage and amenity
values. All OVTs should be covered by a detailed tree risk assessment using From 2,
irrespective of the tree size. For Stonewall Trees, those with a tree diameter at breast
height, measured at 1.3m from the base of the main root on the wall, 95 mm or more
should be covered by a detailed tree risk assessment using Form 2.
♦
Trees on complaint list with structural or health problems - Trees may be under
complaint for various reasons. Detailed tree risk assessment is required only for
outstanding tree complaints related to structural or health problems. It is not
mandatory to conduct a detailed tree risk assessment for a tree under complaint if remedial
action has already been taken or will be taken immediately to alleviate/eliminate the
potential risk.
♦
Mature trees belonging to species with brittle wood structure and having
unsatisfactory health or structural conditions with failure potential - Some tree
species have brittle wood structure which makes them more prone to branch or trunk
failure. These species include Delonix regia (鳳凰木), Erythrina variegata (刺桐),
Alstonia scholaris (糖膠樹), Aleurites moluccana (石栗) and Celtis sinensis (朴樹). Trees
species with brittle wood structure but of smaller mature size such as Bauhinia are not
included in this category. It is not mandatory to conduct detailed tree risk assessment for
a tree species of mature size with brittle branches if no obvious defect that will promote
failure is observed. The objective of highlighting this criterion is to remind Inspection
Officers to pay special attention to tree defects of these species and consider whether a
detailed assessment using Form 2 is required for monitoring purpose.
♦
Trees with major defects or health problems - (refer to Annex C – ‘Pictorial Guide for
Tree Maintenance to Reduce Tree Risk’). - Signs and symptoms of health problems or
defects of varying nature can be found in trees in the course of their lifecycle. Attention
should be paid for the presence of Brown Root Rot Disease, particularly for large mature
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trees. The information on symptoms and control measures for Brown Root Rot Disease is
available in the Development Bureau Tree Management Office’s website
(http://www.trees.gov.hk/en/home/index.html) and the intranet under Cyber Manual for
Greening (http://devb.host.ccgo.hksarg/en/treerisk/index.html) for reference. If the
defects/health problems are of a minor nature, it may not be necessary to mandatorily
conduct a detailed tree risk assessment. If the identified defects or health problems can
be remedied with immediate follow-up measures, for example, removal of hangers and
dead branches, to alleviate the potential risk, it would not be necessary to conduct a
detailed tree risk assessment. In case of doubt, we recommend conducting a detailed
assessment using Form 2 on the subject tree to determine the required risk attenuation
action.
♦
Trees growing in very stressful site conditions with failure potential - Stressful site
conditions may weaken the tree health and/or structural condition and increase the failure
potential. The following examples include:
(a) Confined growing area – For example, shotcreted slopes or concrete footpaths
where tree roots are severely restricted by concrete. Trees in tree pits surrounded by
permeable flexible paving may be excluded from this category.
Confined planting area create stressful condition
Confined planting area create stressful condition
Confined planting area create stressful condition
Dumping around the base of trees can cause root
suffocation and damage to tree trunks
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(b) Trees under cover or low headroom – For example, trees under building canopies
or footbridges where there is limited space for tree crown extension.
Limited
headroom for
tree growth
Tree growing under a footbridge with restricted headroom
♦
Apart from assessing the health condition/structural stability of these trees and identifying
appropriate remedial action, consideration should be given to formulate measures that can
effectively relieve the stressful site condition (e.g. expand the tree planter, transplant the
tree, remove the clutter under the tree, etc.) subject to consideration of the site conditions
and detailed tree inspections.
♦
Anticipated Date of Completion – It is necessary for the tree maintenance departments to
record the anticipated date of completion for the works to be carried out for record,
necessary monitoring and audit purpose.
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4.3.4.6
Guidelines for Tree Risk Management and Assessment
Attached Information
(a) Example of a site plan
Tree Group
Inspection Area
(b) Example of tree photos – overview and close-up photos
♦
Photographic Record – The completed Form 1 should be accompanied by photographic
record showing an overview of the tree group inspection site and diagnostic features of
trees defects observed to facilitate follow-up action on tree problems, and for audit as
well as future monitoring and reference. Sample photos are shown below. Please also
refer to the ‘Guidelines For Photo-Taking During Tree Risk Assessment’ at Annex D
for the detailed requirements. If the tree species cannot be identified on site, the
Inspection Officer can take photos of the tree and seek professional assistance afterwards.
The Inspection Officer may use supplementary sheets to record the details of the tree
species under assessment.
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Site Plan
Photo no.1 - Site condition
Photo no.2 - Ficus hispida to be removed
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4.4
Guidelines for Tree Risk Management and Assessment
Use of Form 2 – Tree Risk Assessment Form
4.4.1
Objective of Form 2
This Form is used for conducting detailed assessment of individual trees that need special
attention. For users with TMIS accounts, the use of Form 2 under the TMIS format is
recommended. Appropriate equipment and hand tools such as binoculars, mallet, hand spade and
probe etc should be used for individual tree assessment when required. The Inspection Officer is
required to give a tree hazard rating with recommendations on follow-up corrective actions to
address the identified defects and tree problems. It is mandatory to carry out Form 2 inspection on
all OVTs and stonewalls trees. Other types of trees that are subject to Form 2 tree inspection are
shown in the chart in 4.4.2.
4.4.2
When to use this Form
Tree Risk Assessment Arrangement
4.4.3
Explanatory notes for Form 2
4.4.3.1
General Information
♦
The “Inspection Officer” undertaking a Form 2 inspection are required to have met both
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Training
(a) have attended and completed the following training courses organised by the TMO:1. Comprehensive Tree Risk Assessment and Management Training Course with
assessment organised; OR
2. Refresher Course with assessment; OR
(b) have undertaken equivalent departmental training recognised by the TMO; OR
(c) have successfully undertaken training programmes recognised by the TMO, such as
Tree Risk Assessment Course and Examination (TRACE) organised by the Pacific
Northwest Chapter of the International Society of Arboriculture (ISA) or Professional
Tree Inspection by LANTRA Awards.
Qualification
Preferably have valid qualifications or certifications awarded by recognised institution or
industry organisation on arboriculture, such as Certified Arborist of ISA, Registered
Arborist (Level 3 or above) of Arboriculture Australia, Technician Member or above of
the Arboriculture Association of the United Kingdom, Accredited Arboricultural
Practitioner of the Hong Kong Institute of Landscape Architects, Professional Diploma
Programme in Arboriculture of the Chinese University of Hong Kong, etc.
Work
Experience
requirements on training AND qualification AND work experience:-
Have at least 2 years of work experience in tree care and are familiar with tree risk
assessment/management.
♦
For outsourced tree inspection works, the consultant/contractor staff can serve as the
“Inspection Officer” to conduct the tree risk assessment, whereas the same requirements
on training AND qualification AND work experience apply.
♦
The “Endorsement Officer” is the supervisory/managerial staff at a rank higher than
Inspection Officer who oversees the tree risk assessment process. To be qualified as
“Endorsement Officers” for Form 2, they should meet the requirements on training /
qualification:-
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Training / Qualification
Greening, Landscape and Tree Management Section
Arrangement
Development Bureau
♦
4.4.3.2
♦
4.4.3.3
Guidelines for Tree Risk Management and Assessment
(a) have attended and completed the following training courses organised by the TMO:1. Comprehensive Tree Risk Assessment and Management Training Course with
assessment organised; OR
2. Refresher Course with assessment; OR
3. Tree Risk Management Training Course with assessment; OR
(b) have undertaken equivalent departmental training recognised by the TMO; OR
(c) have successfully undertaken training programmes recognised by the TMO, such as
Tree Risk Assessment Course and Examination (TRACE) organised by the Pacific
Northwest Chapter of the International Society of Arboriculture (ISA) or Professional
Tree Inspection by LANTRA Awards; OR
(d) have valid qualifications or certifications awarded by recognised institution or
industry organisation on arboriculture, such as Certified Arborist of ISA, Registered
Arborist (Level 3 or above) of Arboriculture Australia, Technician Member or above
of the Arboriculture Association of the United Kingdom, Accredited Arboricultural
Practitioner of the Hong Kong Institute of Landscape Architects, Professional
Diploma Programme in Arboriculture of Chinese University of Hong Kong, etc.
For outsourced tree inspection works, the supervisory/managerial staff of the
consultant/contractor firm can serve as “Endorsement Officers”, whereas the same
requirements on training / qualification apply.
Location information
Please refer to the guidelines for Form 1 as set out in 4.3.4.2.
No. of Tree Trunk and Tree DBH
♦
The tree with multiple trunks shall have each trunk numbered in sequence (i.e. #1,
#2…etc) and the photographic records should include this number.
♦
The Diameter at Breast Height (DBH), measured at 1.3 m above the ground. For
measurement of trees with multiple trunks, please refer to AFCD’s Nature Conservation
Practice Note No. 02 (Rev. Jun 2006) “Measurement of Diameter at Breast Height
(DBH)” at http://www.afcd.gov.hk/english/conservation/con_tech/con_tech.html and
Development Bureau’s Technical Circular (Works) ETWB TC(W)No. 3/2006 “Tree
Preservation” at http://www.devb.gov.hk/TechnicalCirculars.aspx?section=53&lang=1.
4.4.3.4
♦
Tree height
The height of the tree above ground to the top of the tree crown. An indicative estimate
would suffice. For accurate measurement, the use of a clinometer/range pole is
recommended.
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Greening, Landscape and Tree Management Section
Arrangement
Development Bureau
4.4.3.5
♦
4.4.3.6
♦
4.4.3.7
Guidelines for Tree Risk Management and Assessment
Tree spread
The width of the tree crown. An indicative estimate would suffice.
tree crown, please measure the longest axis.
For asymmetric
Age class
A broad indication of the tree age class would suffice.
General condition, Crown condition, Branch condition, Trunk condition and Root
condition
♦
4.4.3.8
Please refer to Annex C - ‘Pictorial Guide For Tree Maintenance To Reduce Tree
Risk’.
Site condition
♦
♦
♦
Site disturbed by construction activities –Self-explanatory.
Soil condition –Self-explanatory.
Restricted root growth area inside dripline – The Inspection Officers should tick the most
appropriate box to reflect the site condition.
♦
Tree location with exposure to wind.
4.4.3.9
♦
♦
4.4.3.10
♦
Target
Please refer to the guidelines for Form 1 as set out in 4.3.4.4
“Use under tree” – The Inspection Officer should tick the relevant use of areas under the
tree. Please specify in the “Others” column as appropriate.
Hazard rating
In tree risk assessment, a hazard is the tree part(s) identified as a likely source of harm.
The hazard rating helps to conclude the overall risk level and decide on the appropriate
follow-up action so as to reduce the risk posed to public safety. The focus is on
identifying and prioritizing appropriate hazard abatement measures for high-scoring trees.
The hazard rating consists of three components:Failure Potential
This relates to the likelihood of failure of a defective tree or
branch.
Size of Part
This relates to the diameter of a defective part and affects the
consequence of failure.
Target Rating
This relates to use of target area which affect the likelihood of
impacting a target by a defective tree part.
Generally speaking, trees with a total score of 9 to 12 warrant special attention.
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Greening, Landscape and Tree Management Section
Arrangement
Development Bureau
4.4.3.11
Guidelines for Tree Risk Management and Assessment
Remedial/Risk Mitigation Measures
♦
♦
♦
To recommend remedial/risk mitigation measures to reduce the potential tree risk.
To provide a record of continuous tree monitoring/management procedure.
The removal of defective parts of the tree, installation of support system, pest and disease
control should be undertaken in a timely manner.
♦
The date of completion of the risk mitigation measures should be recorded when the
required action has been carried out. It is necessary to mitigate the tree risk promptly to
protect public safety.
4.4.3.12 Attached Information
♦
A Site Plan with tree location and tree photo(s) should be attached to the Form 2 in every
case.
♦
Please attach record of tree inspection by resistograph or tomography, if available as
supplementary information.
♦
Photographic Records – The completed Form 2 should be accompanied by photographic
record showing an overview of the site and the trees under assessment. Please refer to
the detailed requirements in ‘Guidelines on Photo-taking of Tree Conditions in the
Process of Tree Risk Assessment’ (Annex D) for details.
Location Plan
Photo no. 2 – Highly restricted growing
condition of the tree
Photo no. 1 - Overview
Photo no. 3 - Wounds on branches
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Greening, Landscape and Tree Management Section
Arrangement
Development Bureau
5.
Guidelines for Tree Risk Management and Assessment
Audit Inspection
5.1
Tree Management departments are required to set up a departmental audit checking
mechanism to ensure that tree risk assessments, whether using Form 1 or Form 2, are properly and
professionally carried out, and that necessary mitigation measures are carried out promptly so as to
protect public safety.
5.2
Departments are required to keep a retrievable and accurate record of the tree risk
assessments, risk mitigation measures and monitoring programme undertaken for the trees under
their management. In carrying out the audit checks, departments should, in particular, review the
accuracy and completeness of the records made as well as the appropriateness of the remedial
measures and the timeliness of their completion. Since tree conditions may change over time, the
audit checks should be conducted as soon as practicable so as to monitor the quality of the
assessment. Any irregularities identified during the audit checks should be followed up promptly.
5.3
Departmental audit checks cover tree risk assessment and follow-up actions carried out
by both in-house staff and outsourced service providers. The “Guideline for Auditing of Tree Risk
Assessment for Tree Management Departments” is available in the Cyber Manual for Greening for
reference.
5.4
If there are complex, doubtful or sensitive cases and/or situations that are likely to arouse
significant public/media concern, colleagues should draw such cases to the attention of the
directorate officers within their departments who, if considered necessary, may approach the Tree
Management Office of the Development Bureau for advice.
5.5
Tree risk assessment and related procedures carried out by departments are subject to
further audit checks by the Tree Management Office of the Development Bureau.
6.
Development Bureau’s Tree Register
6.1
Information on trees on government land which have undergone a detailed tree inspection
(using Form 2) and risk not mitigated is required to be uploaded to the Tree Register at
www.trees.gov.hk to enhance transparency and to facilitate community surveillance of the
conditions of the trees concerned.
6.2
Departments are required to submit the required tree information as well as subsequent
updates to the Tree Management Office in a timely manner for uploading onto the Tree Register for
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Greening, Landscape and Tree Management Section
Arrangement
Development Bureau
Guidelines for Tree Risk Management and Assessment
public information. Reference should be made to “Guidelines on Tree Register – data in and
updating” in the Cyber Manual for Greening.
6.3
Departments should closely monitor the conditions of trees included in the Tree Register
so that timely actions will be taken in response to any change in the tree conditions and relevant
information is sent to the Tree Management Office for updating the Tree Register.
7.
Points to Notes – Remedial/Risk Mitigation Measures and Compensatory Planting
7.1
In the process of carrying out tree risk assessment and remedial/risk mitigation
measures/actions on trees, officers should ensure that no trees are unnecessarily felled or
excessively pruned as stipulated in ETWB TCW No. 3/2006 ‘Tree Preservation’. Departments are
requested to note that tree preservation and conservation remains a primary concern. Reference
should be made to guidelines promulgated by the Tree Management Office, Development Bureau
on proper pruning practices (e.g. ‘General Guidelines on Tree Pruning’ and ‘Dos and Don’ts in
Pruning’). Tree removal should be the last resort.
7.2
The treatment of hazardous trees due to natural causes such as lightning, typhoon,
torrential rain or landslide; or dead/dying/diseased trees; weedy invasive species such as Leucaena
leucocephala which prevent natural succession of indigenous species; and woodland management,
works should follow the requirements in paragraphs 32 and 33 of ETWB TCW No. 3/2006.
Compensatory planting should be encouraged as far as practicable. However, factors such as
sufficient growing space and soil to sustain healthy tree growth, gradient of slopes, etc., should be
considered. The requirement stated in the Technical Circular on ‘Tree Preservation’ (ETWB TC(W)
No. 3/2006) on compensatory planting should be followed.
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